The present invention relates generally to a new composite assembly for transferring heat generated within electronic devices from areas of high heat generation potential to areas of high heat dissipation potential. More specifically, this invention relates to an injection molded thermally conductive elastomeric part having an integral pocket for receiving a heat pipe component.
In the electronics industry, there are various parts and components, which generate heat during operation. For example, it is well known that most computer components generate heat during operation. Various types of electronic device packages and integrated circuit chips, such as the PENTIUM central processing unit chip (CPU) manufactured by Intel Corporation and RAM (random access memory) chips are such devices that generate heat. These integrated circuit devices, particularly the CPU microprocessor chips, generate a great deal of heat during operation, which must be removed to prevent adverse effects on operation of the system into which the device is installed. For example, a PENTIUM microprocessor, containing millions of transistors, is highly susceptible to overheating, which could destroy the microprocessor device itself or other components proximal to the microprocessor.
There are a number of prior art methods to cool heat generating components and objects to avoid device failure and overheating, as discussed above. A block heat sink or heat spreader is commonly placed into thermal communication with the heat-generating surface of the object to absorb and dissipate the heat therefrom. Such a heat sink typically includes a base member with a number of individual cooling members, such as fins, posts or pins, to assist in the dissipation of heat. The geometry of the cooling members is designed to increase the total surface area of the heat sink that is in contact with the ambient air for optimal heat dissipation. The use of such fins, posts of pins in an optimal geometrical configuration greatly enhances heat dissipation compared to devices with no such additional cooling members, such as a flat heat spreader.
To further enhance the overall heat dissipation of an assembly, fans have been installed either internally or externally to increase the airflow over the heat dissipation device. However, these devices consume power and have numerous moving parts. As a result, heat sink assemblies with this type of active devices are subject to failure and are much less reliable than a device that is solely passive in nature.
It has been discovered that as an alternative to the active cooling devices described above, more efficient cooling of electronics can be obtained using passive heat pipes that require no external power source and contain no moving parts. Heat pipes of this type are well-known devices that are employed for efficiently moving heat from one place to another. Generally, the heat pipe is in the form a vacuum-tight vessel having a particular geometric shape, which is evacuated and partially filled with a working fluid. The heat pipe passively transfers heat from a heat source to a heat sink where heat is dissipated. As the heat is conducted into the heat pipe from the heat-generating source, the fluid is vaporized in an evaporator section causing a pressure gradient to develop in the heat pipe. This gradient forces the vapor to flow along the heat pipe to the condenser section, where the vaporized fluid condenses back to its liquid state by giving up its latent heat of vaporization. The working fluid in a liquid state is then returned to the evaporator section to repeat the process of removing the heat generated by the heat source. One method used to achieve cooling by use of a heat pipe places the evaporator section at the lower end and the condenser section at the upper end where the heat pipe is in a substantially vertical position. Once the working fluid has been condensed, the liquid flows by gravity back to the evaporator section. In addition, internal wick structures may be used to assist liquid flow back to the evaporator section through capillary action thereby reducing the effect of gravity on the device.
Alternatively, the heat pipe may be simply filled with the working fluid to create a vapor chamber therein when the liquid is heated by the heat-generating object to its vaporization point. It is well known in the prior art that vaporized water or ammonia is highly thermally conductive and greatly facilitates the transfer of heat.
While heat pipes are highly effective for transferring heat from one point to another, heat pipes are typically tubular in configuration and do not interface well with objects to be cooled. Further, heat pipes, due to their tubular configuration, do not have a significant surface area, preventing them from interfacing well with the ambient air for dissipation of heat. For example, a typical heat pipe may be a tube having a diameter of less than a centimeter while the object to be cooled may be a microprocessor, which is two inches square in shape. Due to the severe mismatch in geometry, affixing such a heat pipe to a microprocessor results in a very inefficient transfer of heat from the large heat generating surface to the small surface area, about one side of the diameter, of a heat pipe. Further, the exposure of the free end, not connected to a heat generating object, to the ambient air is also inefficient because the surface area of the diameter of the heat pipe is relatively small thus making the dissipation of heat even more inefficient.
In order to enhance the efficiency for the interface ends of the heat pipe, it is desirable to cast a heat sink assembly or overmold a thermally conductive configuration about the heat pipe to increase the overall contact surface area. However, in so doing, there is a serious risk of damage to the heat pipe during the casting or molding process. If the casing of the heat pipe is cracked or split during formation of the overmolded configuration, the heat pipe media will leak and the heat pipe will not operate properly, resulting in a deleterious effect on the thermal conductivity of the overall heat dissipation device.
In view of the foregoing, there is a demand for a heat pipe construction and a method for manufacturing such a construction that is less expensive than the prior art yet provides superior heat dissipation. There is a demand for a passive heat pipe construction with no moving parts that can provide heat dissipation without the use of active components. In addition, there is a demand for a method of manufacturing a heat pipe construction that enables a heat pipe to be incorporated into an assembly that includes additional heat dissipating material, without the risk of damage to the heat pipe itself.
In this regard, in accordance with the present invention, a composite assembly that has the capacity to conduct heat from an area of high heat generating potential to an area of high heat dissipation potential is provided. One component of the part is net shape injection molded from a thermally conductive elastomeric material to create the required geometry for the proper interfacing and heat dissipating configurations and has an integrally molded channel to receive a heat pipe. The molded component is formed from a base elastomeric matrix material that is loaded with thermally conductive filler. The base material is mixed with the filler and injected into a mold cavity to form the outer geometry of the assembly. Within the geometry of the part an integral channel is formed that is capable of receiving a heat pipe. Since the heat pipe channel is formed in the elastomeric composite, the walls of the channel have resilient and conformable properties.
The geometry of the channel is formed in such a manner so as to have an opening that is slightly smaller that the outer cross-sectional dimensions of the heat pipe. When the heat pipe is pressed into the channel a portion of the elastomeric material is compressed and the reactionary force of the compressed material firmly presses the elastomer into thermal communication with the outer surface of the heat pipe. This allows the outer component of the assembly to be net shape molded into virtually any required geometric configuration, including very thin profiles that were previously unattainable in the prior art using traditional over molding methods. In addition, the manner in which the elastomer mates to the surface of the heat pipe reduces junction resistance between the surface of the heat pipe and the outer component, thereby eliminating the need to use thermally conductive glues, greases or conformable thermal interfaces to assemble the part.
Another feature of the present invention is the fact that the elastomeric portion of the present invention has geometry that is flexible and conformable. This allows the construction of a flexible heat pipe assembly that is quite useful in compact assemblies with limited space through which to conduct waste heat. Also, the conformability of the elastomeric material allows it to be installed directly in contact with the heat generating surface and the heat-dissipating surface without the additional requirement of an interface pad. The elastomeric material is capable of overcoming and conforming to the slight surface imperfections that occur from the fabrication techniques of those surfaces thus resulting in superior thermal interface.
Further, the method used in manufacturing the present invention is superior In that it eliminates several steps as compared to the prior art. By first net shape molding the outer component into the desired geometric configuration additional steps associated with machining and polishing the parts into the finished shape are eliminated. Also, by pressing the heat pipe into the conformable channel after the part is formed, the heat pipe can be fully charged before incorporation into the assembly.
A single heat pipe is preferably employed but multiple heat pipes may be embedded within the construction of the present invention. Alternatively, other heat transfer conduits may be employed instead of a heat pipe, such as copper rods or formed copper strands. In addition, optional flat contact ends are can be provided in the overall part geometry proximal to where the ends of the heat pipe reside in its installed position to achieve greatly improved thermal interface results in a manner that is far less expensive than soldering a heat pipe to a heat spreader.
It is therefore an object of the present invention to provide an improved composite heat dissipation composite assembly that can provide enhanced heat dissipation for a heat generating component or object. It is a further object of the present invention to provide a heat pipe construction device that has no moving parts. Another object of the present invention is to provide a composite heat pipe construction that is completely passive and does not consume power. A further object of the present invention is to provide a heat pipe construction that inexpensive to manufacture. It is yet another object of the present invention to provide a conformable elastomeric heat sink geometry into which a heat pipe can be installed after the part is molded with out the requirement of thermal interfaces or adhesives. A further object of the present invention is to provide a method of manufacturing a conformable composite heat pipe construction that is moldable and is easy to assemble manufacture.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.